1. Field of the Invention
The present invention relates to a chip-type piezoelectric resonance component which is suitably surface-mounted on a substrate, for example, and more particularly, it relates to a chip-type piezoelectric resonance component employing an energy-trap piezo-resonator.
2. Description of the Background Art
In general, a resonator utilizing an expansion vibration mode of an angular piezoelectric plate, that utilizing a length vibration mode of a bar type piezoelectric body, or a piezoelectric tuning fork type resonator is employed as a piezo-resonator for the kHz band.
In such a piezo-resonator, a resonance part vibrates upon application of a voltage. In order to form the piezo-resonator as an actual component, therefore, it is necessary to support the piezo-resonator for allowing resonance. It is possible to mechanically hold an energy-trap piezo-resonator in regions other than its resonance part since vibrational energy is trapped in the resonance part. In view of application to a product, therefore, the energy-trap piezo-resonator is superior to other types of piezo-resonators, and hence such an energy-trap resonator is desired also in relation to a piezo-resonator for the kHz band.
In a resonator utilizing an expansion vibration mode or that utilizing a length vibration mode which is known as a general kHz band piezo-resonator, however, it is impossible to trap vibrational energy. As shown in FIG. 1, therefore, a piezo-resonator 191 utilizing a length vibration mode is held by spring terminals 192 and 193 holding vibration nodal points therebetween. Also in an angular plate type piezo-resonator utilizing an expansion vibration mode which cannot trap energy, nodal points of the resonator are held between spring terminals. In the piezo-resonators for the kHz band utilizing the expansion and length vibration modes, therefore, the structures of the components are so complicated that it is extremely difficult to form miniature chip-type components which are surface-mountable.
In a piezoelectric tuning fork type resonator 196 comprising a piezoelectric plate 194 which is polarized along its thickness and provided with slits 194a to 194c, and vibrating electrodes 195a (that on a back surface side is not shown) which are formed on both major surfaces of the piezoelectric plate 194 around the central slit 194b as shown in FIG. 2, on the other hand, energy is trapped in its vibrating part. Therefore, the resonator 196 can be formed as a surface-mountable chip component since its characteristics remain unchanged when this resonator 196 is held in portions close to edges 194d and 194e of the piezoelectric plate 194, for example.
In the piezoelectric tuning fork type resonator 196, however, the ensurable bandwidth is merely about 2% of the resonance frequency due to restriction on its mode, although the energy can be trapped. In the market, on the other hand, a broadband piezo-resonator is strongly required also in relation to the kHz band. The piezoelectric tuning fork type resonator 196 cannot satisfy such requirement.